Novel Triarylamine-Based Hole Transport Materials: Synthesis, Characterization and Computational Investigation

Three novel triarylamine-based electron-rich chromophores were synthesized and fully characterized. <b>Compounds 1</b> and <b>2</b> were designed with electron-rich triphenylamine skeleton bearing two and four decyloxy groups namely, 3,4-bis(decyloxy)-<i>N,N</i>-diphenylaniline and <i>N</i>-(3,4-bis(decyloxy)phenyl)-3,4-bis(decyloxy)-<i>N</i>-phenylaniline, respectively. The well-known electron-rich phenothiazine was introduced to diphenylamine moiety through a thiazole ring to form <i>N,N</i>-bis(3,4-bis(decyloxy)phenyl)-5-(10<i>H</i>-phenothiazin-2-yl)thiazol-2-amine (<b>Compound 3</b>). These three novel compounds were fully characterized and their UV-vis absorption indicated their transparency as a favorable property for hole transport materials (HTMs) suitable for perovskite solar cells. Cyclic voltammetry measurements revealed that the HOMO energy levels were in the range 5.00-5.16 eV for all compounds, indicating their suitability with the HOMO energy level of the perovskite photosensitizer. Density functional theory (DFT) and time-dependent DFT (TD-DFT) have been used to investigate the possibility of the synthesized compounds to be utilized as HTMs for perovskite solar cells (PSCs). The computational investigation revealed that the hole mobility of <b>Compound 1</b> was 1.08 × 10^-2 cm² V^-1 s^-1, and the substitution with two additional dialkoxy groups on the second phenyl ring as represented by <b>Compound 2</b> significantly boosted the hole mobility to reach the value 4.21 × 10^-2 cm² V^-1 s^-1. On the other hand, <b>Compound 3</b>, in which the third phenyl group was replaced by a thiazole-based phenothiazine, the value of hole mobility decreased to reach 5.93 × 10^-5 cm² V^-1 s^-1. The overall results indicate that these three novel compounds could be promising HTMs for perovskite solar cells.